Image storage tube multiplier element



Sheet of 2 April 22, 1969 R. w. DECKER IMAGE STORAGE TUBE MULTIPLIERELEMENT Filed Sept. 14. 1965 WITNESSES April 22, 1969 R. w. DECKER IMAGESTORAGE TUBE MULTIPLIER ELEMENT sheet 3 ofz' med sept. 14, 1965 INPUTSIGNAL TO BE STORED SECOND cRossovER- \/\F|RsT cRossovER o t lzomm zoomwINCIDENT PRIMARY ELECTRON ENERGY (ELECTRON VOLTS) United States Patent O3,440,470 IMAGE STORAGE TUBE MULTIPLIER ELEMENT Richard W. Decker,Baltimore, Md., assignor to Westinghouse Electric Corporation,Pittsburgh, Pa.I a corporation of Pennsylvania Filed Sept. 14, 1965,Ser. No. 487,228 Int. Cl. H01j 43/00 U.S. Cl. 313-103 3 Claims ABSTRACTOF THE DISCLOSURE This invention relates to image storage devices andmore specifically to storage devices in which information may be storedas a pattern of charges and then extracted at a later time.

This invention is more particularly directed to a storage multiplierelement which may be incorporated into an image storage device forstoring a pattern of charges and intensifying the output signal derivedfrom said pattern of charges. Further, this invention relates to amethod of manufacturing an improved multiplier element.

One particular application of this invention is in an image correlationdevice such as described in the copending application entitled, Methodand Apparatus for Performing Image Correlation, Ser. No. 470,108 filed,July l, 1965, by A. S. Jensen and assigned to the assignee of thisinvention. Generally, correlation refers to the technique of comparingtwo images and deriving an output signal related to the displacement ofthe elements within the two images. Correlation is performed in thedevice described in the above-mentioned copending application by firststoring a pattern of charges corresponding to the first image on astorage target element. Next, an electron beam or image representing thesecond image is directed toward the storage element and an output signalis obtained by collecting the second electron image which has beeneffectively modulated or influenced by the pattern of chargesrepresenting the first image. Further, by displacing the second electronimage with respect to the pattern of charges stored upon the storageelement, maximum or minimum values may be obtained and a comparisonbetween the first and second images is provided as a function of thisdisplacement. The electron image device as described in theabove-mentioned copending application includes a photocathode elementfor converting the light radiation from the first and second scenes intocorresponding electron images which are in turn directed upon thestorage element. In one particular embodiment, the storage elementcomprises a conductive backplate upon which there has been disposed aplurality of dielectric elements capable of being charged to a form apattern of charges corresponding to the first electron image. Asexplained above, the second scene is then directd upon the photocathodeelement and a corresponding second electron image is deflected acrossthe target element as by an electromagnetic coil disposed between thephotocathode element and the storage target element; an output signal isderived from the electrically conductive backplate upon which isdirected the second electron image that has been modulated by thepattern of charges stored upon the dielectric elements.

3,440,470 Patented Apr. 22, 1969 lCe A problem related to this type ofimage device and more particularly to pholocathode elements occurs whena particularly intense light beam is focused on a portion of thephotocathode element. More specifically, the intense light beam causesthe photoemissive layer of the photocathode element to emit acorrespondingly intense beam of electrons. The beam of electrons isdrawn as a current through the conductive layer of the photocathodeelement and is emitted as a beam of electrons from the photoemissivesurface. Typically, the electrically conductive layer presents a highresistance in the order of thousands of ohms per centimeter to thecurrent drawn therethrough. Even if only a microamp or less current isdrawn by the emitted photoelectron beam, a potential in the order ofseveral hundred volts may be developed over a portion of theelectrically conductive backplate. As a result, the point of electronemission upon the photocathode element may be disposed at a potential ofseveral hundred volts whereas the peripheral portions may be disposed atground potential. In order to focus the electron beam emitted by thephotocathode element it is necessary to dispose other electrodes aboutthe path of the electron beam with correspondingly increasing positivepotentials applied thereto. However, if a potential of several hundredvolts is developed upon a portion of the face of a photocathode element,the focusing voltages between the photocathode element and theaccelerating electrodes is radically changed and the electron imagegenerated by the photocathode element will no longer be focused upon thestorage element.

' In another application, this invention may be applied to storage type,cathode ray display tubes. In general, the display type storage tubeconsists of a perforate storage grid member which controls the electronflow from a flood-type electron gun to a luminescent screen. A spacedistributed charge image is produced on the surface of the storage gridfby an intensity modulated, scanning electron beam. The charge image sorecorded on the storage grid controls or modulates the flow of electronsfrom the flood type reading gun to the screen; thus a visual light imageof the charge pattern is produced on the display screen.

In a display type storage tube, the reading and writing electron beamsare produced by typical electron guns which, in contradistinction to theimage devices for correlation as described above, are capable ofproviding an electron beam with ample current density without fear ofbeing defocused as it lands upon the luminescent screen. However, inorder to provide suflicient illumination from the screen, the chargepattern disposed upon the storage grid member is written by a highdensity electron beam. Of necessity, a high density electron beam has agreater width or spot size which prevents the deposition of a highresolution pattern of charges upon the storage grid member. Further, inorder to achieve the desired degree of brightness, the flood electronbeam as emitted from the reading gun must be accelerated under a highvoltage in order to bombard the displace screen with sufficient energy.Thus it may be understood that the reading electron beam may not besufficiently controlled or modulated by the pattern of charges andresultant deformities may be introduced in the visual light patternprojected from the luminescent screen.

Accordingly, an object of the present invention is to provide a new andimproved electron image device and storage target element therefor.

Another object of this invention is to provide a new and improvedstorage target element capable of providing an intense output signal.

It is another object of this invention to provide a new and improvedelectron image device capable of maintaining the focus of an electronimage as emitted by a photocathode element even while sensing intenselight radiation.

It is a still further object of this invention to provide a new andimproved electron image device capable of storing a high resolutionpattern of charges and displaying an intense light image correspondingto said pattern of charges.

It is another object of this invention to provide a novel method offorming a multiplier element with a plurality of tubular elements havinga uniform configuration and a surface exhibiting uniform secondaryemissive characteristics.

Briefly, the objects of this invention are accomplished by providing anelectron image device incorporating a target element including at leastone tubular element having an interior surface capable of emittingsecondary electrons in response to an electron bombardment and a storagemeans such as a layer of dielectric material disposed upon the entranceportion of the tubular element. Typically, a plurality of the tubularelements are combined together so that an electron image may be storedupon the layer of dielectric material and a multiplied output vsignalmay be obtained by bombarding the interior surface of the tubularelements with an electron beam that has been modulated by said patterncharges. Further, the electron image device of this invention includes ameans for producing an electron beam to be directed upon the layer ofdielectric material of the storage elements and a means for collectingthe intensified electron beam generated within the tubular element ofthe target element.

In one exemplary embodiment of this invention, an electron image deviceis provided with a photocathode element for converting a first andsecond light image incident thereon into corresponding electron images.The storage target lement as described above is disposed between thephotocathode element and a means such as an electroconductive plate forreceiving the electron beam as intensified by the storage targetelement. Further, there is disposed about and between the photocathodeelement and the storage element a means for deliection such as anelectromagnetic coil to displace the electron image representing thesecond scene with regard to the pattern of charges stored upon thestorage element and representing the first scene.

In another exemplary embodiment of this invention, an electron imagedevice is provided with an electron gun for emitting a pencil like beamof electrons onto the above-described target element and a luminescentdisplay screen for displaying a visual image corresponding to thepattern of charges stored upon the target element. Further, a secondelectron gun is provided to direct a flood beam of electrons onto thetarget element; the ood beam of electrons is modulated by the pattern ofcharges disposed upon the storage element and intensified by repeatedbombarding against the interior surface of the tubular elements. Theintensified electron beam is then directed to the display screen andconverted into a visual light image.

It is a further aspect of this invention to provide a new and novelmethod of manufacturing a multiplier element having a plurality ofuniformly spaced tubular elements having a regular, definedconfiguration and presenting an interior surface with uniform secondaryemissive characteristics. In accordance with the teachings f one aspectof this invention, this method includes the steps of forming a uniformfilament having a smooth exterior surface. Next, the surface of thefilament is oxidized to provide a material having the property ofemitting secondary electrons in response to a bombardment of primaryelectrons. The interior portion of the filament is removed so as toexpose the surface region having the property of secondary emission.Lengths of the filament are joined to each other and are cut to form acomposite multiplier element as described above. In one illustrativeembodiment of this invention, a core made of Ia suitable material suchas nylon is coated with a thin aluminum or magnesium coating as byevaporation. Next, the aluminum coating is oxidized and the filament iscoated with an adhesive material. Next, while the adhesive materialremains in an unset condition, the filament is wound about a reel andthe adhesive material hardened. Finally, the wound filament is cut intosections yand the inner core is removed by an etching solution tothereby provide a multiplier element having a plurality of regularlyformed tubular elements. Alternatively a solid aluminum wire could beused, in this method the outside surface of the aluminum is wireoxidized and the center portion is then removed by an appropriatereactant such as hydrochloric acid.

Further objects and advantages of the invention will become moreapparent as the following description proceeds and features of noveltywhich charactrize the invention will be pointed out in particularity inthe claims annexed to and forming a part of the description.

For a better understanding of the invention, reference may be had to theaccompanying drawings, in which:

FIGURE l is a schematic illustration of Ian electron image storagedevice incorporating the teachings of this invention;

FIG. 2 is an enlarged, sectional view of the Storage multiplier elementwhich has been incorporated within the device as shown in FIG. l;

FIG. 3 is an enlarged, sectional View taken Kalong the line III-III ofFIG. 2 of the storage multiplier element which has been incorporated inthe device of FIG. 1;

FIG. 4 shows a sectioned view of an alternative embodiment of theelectron image device of this invention;

FIG. 5 is a characteristic curve of effective secondary emission ratioof a dielectric material as a function of the energy of bombardingelectrons upon the surface of the material; and

FIG. 6 is a schematic diagram showing a method of fabricating a filamentinto a multiplier element in accordance with the teachings of thisinvention.

Referring now to the drawings and in particular to FIG. l, there isshown an image storage device 10 incorporating a storage multiplierelement 32 in accordance with the teachings of this invention forelectronically performing correlation between the two images. The imagestorage device 10 comprises an envelope 12 with a cylindrical portion 14made of a suitable insulating material such as glass and enclosed uponone end by a face plate 16 made of a suitable light transmissivematerial such as glass. A photocathode element 18 is disposed on theinterior surface of the face plate 16 and includes a photoemissivecoating 20` which is sensitive to the input radiation and a suitableelectrically conductive contact formed as a layer 22. In the instancewhere the input radiation is visible light, the photoemissive coating 20may be made of a suitable material such as cesium antimony which may beevaporated onto the conductive layer 22 by Well known techniques.

Further, an electron accelerating means 24 is provided along the lengthof the inner surface of the cylindrical portion 14 in order toaccelerate the electrons emitted by the photocathode element 18. Theelectronic accelerating means 24 includes a first spiral electrode 26adjacent the photocathode element 18 having one end thereof connectedexteriorly of the envelope 12 to ground. A second spiral electrode 28 isdisposed at the outer end of the cylindrical portion 14 of the envelope12 and is electrically connected exteriorly of the envelope 12 to apotential source 40. An equipotential electrode 30 is disposedintermediate of and in electrical connection with the first and secondspiral electrodes 26 and 28. Typically, the first and second spiralelectrodes 26 and 28 and electrode 30 may be formed by first evaporatinga thin layer of approximately A in thickness of a suitable electricallyresistant material such as chromium upon the interior surface of thecylindrical portion 14. Next, portions of this thin layer may be removedas iby a lathetype scraping tool to form the first and second spiralelectrodes 26 and 28.

Within the opposite end of the image storage device 10, there isdisposed the storage multiplier element 32. A mes-h electrode 34 isdisposed in a plane parallel to and spaced from the surface of thestorage multiplier element 32. Further, a collector electrode 36 isdisposed on the other side of the storage multiplier element 32 in orderto receive an electron beam directed through the element 32. Thecollector electrode 36 is in turn connected through an impedance 42 anda potential source 44 to ground, and an output signal is derived fromthe voltage developed across the impedance 42. Further, the meshelectrode 34 is connected externally of the envelope 12 as by aswitching7 means 37 to either of potential sources 38 and 39 which arein turn connected to ground.

Referring now to FIGS. 2 and 3, a specific embodiment of the storagemultiplier element 32 will be shown. The storage multiplier element 32includes a plurality of tubes or tubular means 46 joined together sothat the axis of each tube is disposed parallel with each other.Further, the tubes 46 are bound together as by an adhesive 50 such as analuminum oxide which has been applied by a slurry technique and thendryed in a non-oxidizing atmosphere. Further, the interior surface ofthe tube 46 is made of a suitable material such as aluminum oxide whichwill present a secondary emissive surface 48 to electrons which aredirected wit-hin the tubes 46 as shown in FIG. 2. Further, theinterstices formed by the entrance portions (or means) of the tubes 46are coated with conductive layers 52 and 56 of a material such as goldto a depth in the approximate range of 500 to 1000 A. In addition, alayer 54 of a suitable storage dielectric material such as magnesiumIfluoride is deposited upon the conductive layer 52. It is noted thatthe apertures as defined by the tubes 46 extend through the conductivelayers 52 and 56 and the layer 54 of the dielectric storage material. Aswill be explained later, incident primary electrons will be directedwithin the tubes 46 and Will be accelerated by a potential appliedbetween the conductive layers 52 and 56 to thereby be repeatedlybombarded against the secondary emissive surface 48. In order to achieveelectron multiplication within the tubes 46, the ratio of the axialdimension to the diameter of the tubes 46 should be maintained in excessof l0 to 1. However, in order to achieve electron gains which are highenough to be inserted in most tubes, a ratio of axial dimension to thediameter of the tube must exceed 40. It is noted that with a diameter of1/1000 inch and a diameter to length ratio of 100 that an electronmultiplication in the order of 106 has been achieved.

Referring now to FIG. l, the conductive layer 52 of the storagemultiplier element 32 is connected through a switching means 58 througheither of the potential sources 60, 62 or 63 to ground. In addition, theconductive layer S6 is connected externally of the envelope 12 through apotential source 64 to ground. Further, a suitable lens system y66 forfocusing the radiations emitted from a scene 68 onto the photocathodeelement 18. A shutter 70 is disposed between the lens system 66 and theface plate 16 of the image storage device 10. In particular, the shutter70` includes a movable element 72 which may be actuated from a closedposition 1 to an open position 2 in order to allow the radiations to befocused by the lens system 66 unto the photocathode element 18. Asuitable focusing means such as an elongated magnetic coil 76 isdisposed along the length of the envelope 12 to focus the electronsemitted by the photocathode element 18 onto the storage multiplierelement 32. Further, a deflection means 78 such as a standard imageorthicon deflection coil is disposed about the cylindrical portion 14 ofthe envelope 12; more particularly, the defiection means 78 is disposedabout the equipotential electrode 30 to insure that no rotationalcomponent is imposed upon the electron beam emitted by the photocathodeelement 18. Within the area defined by the electrode 30, the potentialfield established by the electrode remains substantially constant; as aresult, the field generated by the deflection means will only impart alinear motion to the electron beam being directed upon the storagemultiplier element 32. Further, a light source 74 such as a lamp isdisposed to uniformly excite and iiood the photocathode element 18 withlight.

The operation of the image storage device 10 as shown in FIG. 1 requiresthe performance of a four part cycle. The four steps of the operationinclude (l) priming, (2) exposure to a first image, (3) exposure to asecond image, and (4) erasing.

(1) Prz'ming.-During the first step of the operating cycle, theconductive layer 52 of the storage multiplier element 32 is set at apotential with respect to that of the cathode element 18 ofapproximately l2 volts positive. This is accomplished by connecting theconductive layer 52 to the potential source 60 through the switchingmeans 58 (position 1). The movable element 72 of the shutter 70 isdisposed in a closed position (i.e. position 1) and the light source 74is energized to cast a uniform light upon the photocathode element 18.In turn, the photocathode element 18 emits a uniform electron beam whichis accelerated by the accelerating means 24 to flood the storagemultiplier element 32.

As is well understood in the art, electron bombardment upon a dielectricstorage material will cause the dielectric material of layer 54 to emitsecondary electrons. Referring now to FIG. 5, it may be seen that in theregion below first crossover and in the region above second crossoverthat less than one secondary electron will be emitted in response to oneincident primary electron. In the region between first crossover andsecond crossover, which points are determined by the characteristics ofthe particular storage material, more than one secondary electron willbe emitted for each incident primary electron. It is noted that the l2volts applied to the conductive layer 52 to accelerate the electronsemitted by the photocathode element 18 is below the first crossoverpotential of the storage material of which the layer 54 is made. As aresult, the surface of the layer 54 is driven negatively due to theaccumulation of negative electrons. Thus, in this exemplary method ofoperating the image storage device 10, the surface of the layer 54 hasbeen set at a potential of approximately 12 volts negative with respectto the potential of the conductive layer 52.

(2) First exposure-After the priming step, the switching means 58 isdisposed in its second position whereby the conductive layer 52 isconnected to the potential source 62 which is approximately 22 voltspositive with respect to ground. Due to the capacitive action betweenthe conductive layer 52 and the surface of the layer 54, the surface ofthe layer 54 is set at a potential of approximately 10 volts positivewith respect to ground. Next, the movable element 72 is moved to theopen position (i.e. position 2) and the radiations from the scene 68 arefocused as by the lens system 66 onto the photocathode element 18. Thephotocathode element 18 converts the radiation image into acorresponding electron image which is accelerated by the means 24 ontothe storage multiplying element 32.

It is noted that during this writing step, that the voltage applied tothe conductive layer 52 is likewise below the first crossover potentialof the storage material of which the layer 54 is made. As a result, theelectron image as emitted by the photocathode element 18 will tend todrive those bombarded portions of the layer 54 negatively due to theaccumulation of electrons. After the electron image corresponding to thefirst image from the scene 68 has been integrated for a sufficientperiod of time upon the layer 54, the shutter 70 is closed (i.e.position 1). At

this point in the operating cycle, those portions of the layer 54 whichhave been bombarded with primary electrons will be charged to a level ofapproximately 7 volts positive with respect to ground or volts negativewith respect to the potential of the conductive layer 52. Further, thoseportions of the layer 54 which have not been bombarded with the primaryelectrons will be charged to a level of approximately 10 volts positivewith respect to ground or l2 volts negative with respect to thepotential of the conductive layer 52.

(3) Second exposure-After a charge pattern has been disposed upon thesurface of the layer 54 corresponding to the first image, the imagestorage device 10 may be switched to receive the second image. This maybe accomplished by disposing the switching means 58 in its firstposition so that the electrically conductive layer 52 is connected tothe potential source 60 of a value of approximately l2 volts positivewith respect to ground. Due to the capacitive coupling between theconductive layer 52 and the surface of the layer 54, the surface of thelayer 54 which has been charged during the first exposure is disposed ata potential of approximately 3 volts negative with respect to ground;those portions of the layer 54 which have not been charged are broughtto a potential of approximately ground.

Referring now to FIG. 2, there is shown a cross sectional view of thestorage multiplier element 32. As explained above, portions of the layer54 have been disposed between 3 volts negative with respect to groundand ground potential. It may be understood that other portions of thelayer 54, as shown in FIG. 2, may be charged to voltages intermediatezero and 3 volts negative with respect to ground to reliect variousshades of the scene 68. As can be seen in FIG. 2, the portions of thelayer S4 which have been charged negatively generate equal potentialsurfaces that tend to cut down the area through which the electronsemitted by the photocathode element 18 can be directed into the tubes46. As the portions of the layer 54 are driven more negatively, thenegative equal potential surfaces spread out and tend to prevent theentrance of the electron beams into the tubes 46. Thus, where there hasbeen deposited a more negative charge upon the layer 54, the negativeequal potential surfaces overlap with each other and less electrons areallowed to enter the tubes 46; on the other hand where a more positivecharge has been disposed upon the layer 54, the negative equal potentialsurfaces provide a greater passage therebetween and a greater number ofelectrons are allowed to enter the tubes 46. It is particularly notedthat due to the negative charge disposed on the layer 54 that theelectrons emitted from the photocathode element do not land on the layer54 and that the charge pattern established during the first exposurewill remain and continue to iniiuence or modulate the electron beam fromthe photocathode element 18.

Once the electrons have entered within the tubes 46, the electricalfield as established between the conductive layers S2 and 56 tend toaccelerate the electrons along the axial length of the tubes 46. As theelectrons move along the length of the tubes 46, they tend to bombardthe secondary emissive surfaces 48 with an energy sufficient to producemore than one secondary electron per incident primary electron. As aresult, the electron beam modulated by the pattern of chargesdistributed upon the layer 54 is successively multiplied by repeatedbombardment against the secondary emissive surface 48 and a greatlymultiplied electron current is emitted from the plurality of tubes 46 tobe collected upon the collector electrode 36. Typically, a voltage ofapproximately 2,000 volts positive with respect to ground is applied tothe conductive layei 56 in order to accelerate the electrons through thetubes 46. Further, a potential of approximately 2,050 volts positivewith respect to ground is provided by the potential source 44 upon thecollector electrode 36 to thereby attract the electron image derivedfrom the storage multiplier element 32.

During the second exposure, the radiation from the scene 68, theelements of which have changed since the first exposure, is directedonto the photocathode element 18; an electron image corresponding to thesecond radiation image is directed over substantially the entire area ofthe storage multiplier element 32. Since the storage multiplier element32 is not being scanned as in a typical television readout tube by anarrow pencil beam electron but rather by a fiood type beam of electronsthe distribution of which corresponds to the radiation from the scene68, the signal derived from the collector electrode 36 is aninstantaneous summation of all the electron currents directed throughthe plurality of tubes 46 and collected by the electrode 36. In otherwords, the signal derived from the collector electrode 36 represents anintegration of the various currents derived from each portion of thecollector electrode 36. Further, each of the electron currents directedupon the electrode 36 is in turn a function of the charge stored uponthe layer 54 of dielectric storage material and, further, a function ofthe density of electrons emitted by the photocathode element 18 duringthe second exposure. This may be represented mathematically as:

where 2(x,y) represents the electron image directed upon the storagemultiplier element 32 during the second exposure and q1(x,y) representsthe charge distribution stored upon the storage layer 54 during thefirst exposure. Thus, it may be understood that the output signalderived from the collector electrode 36 accurately represents acorrelation function of the first and second scenes taken respectivelyduring the first and second exposure of the image storage device 10.

In order to sense a change in the composition of scene 68 between thefirst and second exposures, the pattern of charges as stored upon thelayer 54 and the electron image representing the scene during the secondexposure should be varied or displaced with respect to each other.Referring to FIGURE 1, there is shown an exemplary means for obtaining alinear displacement of the electron image emitted by the photocathodeelement 18 during the second exposure. In particular, a current source(not shown) supplies a sawtooth current wave to the deliection means 78which in turn provides a deflection field across the cross-section ofthe envelope 12. The electron image is thereby displaced in accordancewith the electric field generated by the means 78 and the points ofincidence of the electron image upon the layer 54 will thereby vary in alinear manner. It is noted that the defiection means 78 is disposedabout the equi-potential electrode 30 so that the electromagnetic fieldgenerated by the means 78 does not interact with a changingelectrostatic field to produce an undesired rotation of the electronbeam emitted from the Iphotocathode element 18.

When two scenes which are identical to each other are viewed in a manneras described above, a minimum (or a maximum, depending upon the polarityof the signals) output signal will be derived from the collectorelectrode 36 at that point where there is no displacement between thescenes. As the second image is displaced from the first image, as by themeans 78, the output signal will correspondingly be decreased due to thelack of correspondence between the elements of the two images beingcorrelated with each other. It may be understood that where the imagesor scenes viewed upon the device 10 are not identical but where there isa deviation due to the movement of some object within the second image,there will be achieved a minimum (or maximum) output signal where thereis the closest correspondence between the elements of the first andsecond images. The degree to which the first and second images aresimilar to each other is indicated by the scope, the arnplitude, and theamount of displacement required to derive the minimum output signal. Thecurve or curves so obtained may be compared with correlation curves forknown changes in the image to thereby determine the nature of themovement in the second image. Further, the output signal derived fromthe collector electrode 36 may be viewed upon a display device such asan oscilloscope (not shown) which has in addition been connected to thecurrent source attached to the means 78 to thereby provide a visualdisplay of the output signal Vas a function of the displacement betweenthe first and Isecond images.

For a further explanation of the structure and operation of a device forperforming correlation between two scenes, reference is made to theabove-mentioned copending application of A. S. Jensen.

(4) Erasing-In order to perform an additional correlation operation, itis necessary to remove the pattern of charges which have been disposedupon the layer 54 of storage dielectric material. In order to accomplishthis fourth step, the switching means 58 is disposed in a third positionin order to apply the potential source 63 to the conductive layer 52 ofthe element 32. Further, the switching means 37 is connected in a secondposition in order to connect the mesh electrode 34 to the potentialsource 39. During the erasing step, it is desired to bombard the layer54 with electrons accelerated by a potential above the first cross-overof the storage material of the layer 54. As explained above, incidentelectrons which have been accelerated to a potential between the firstand second cross over potentials will cause a dielectric material toemit more secondary electrons than the number of incident primaryelectrons. In a typical operation of the storage multiplier element 32,the potential source 63 is set at a value of approximaately volts andthe potential source 39 is set at a value of approximately 310 volts.Further, the light source 74 is energized and the light therefrom isfocused upon the photocathode element 18. A resultant electron beam isaccelerated by the potential applied to the conductive layer 52. As theelectron beam emitted by the photocathode element 18 strikes the layer54, secondary electrons are emitted and collected by the mesh electrode34; as a result, there is a loss of electrons and the surface of thelayer 54 is driven positively to a voltage approaching that applied tothe mesh electrode 34. At the end of this step, the entire surface ofthe layer 54 is charged positively and the pattern of charges disposedthereon during the first exposure is removed.

Further, it may be understood that in order to write a pattern ofcharges upon the layer 54 of the element 32 it would be necessary toprime the surface of the layer 54 as described above. Typically, thismay be performed by displacing the switching means 58 in its firstposition and repeating the process as outlined above.

Referring now to FIG. 4, there is shown an image storage display device110 comprising an evacuated envelope 112 of suitable shape andconfiguration. Positioned at one end of the envelope 112 are disposed aplurality of electron guns 114 and 116. In the specific embodimentshown, the electron gun 114 is provided for generating a pencil typeelectron beam which may be used to scan the entire surface of a storagemultiplier element 132 positioned at the opposite end of the envelope112. It is noted that the stored multiplier element 132 is substantiallyidentical to that described with regard to FIG- URES 2 and 3. The secondelectron gun 116 is centrally located within the envelope 112 to providea flood election beam over the entire surface of the storage multiplierelement 132.

The electron gun 114, which may be referred to as a write gun, iscomprised of a cathode element 118, a control grid 120, and beam formingand accelerating electrodes 122, 124 and 126. Electrostatic deliectionmeans in the form of two pairs of plates 130 and 134 are provided infront of the beam forming electrodes for deflecting the electron beamgenerated within the electron gun 114 so as to scan a raster on a layer156 of a storage dielectric material. Suitable voltages are applied tothe electrodes 118, 120, 122, 124 and 126 in a well known manner inorder to provide proper focusing and accelerating of the electron beam.The cathode element 118 of the write electron gun 114 is connected bymeans of a lead-in conductor to the negative terminal of a potentialsource 136. The control grid 120 is connected by means of a lead-inconductor to a video information source 138. The control grid 120 isalso connected through a resistor to the negative terminal of apotential source 142. The potential source 142 may be of the order ofap-- proximately 60 volts with the positive terminal of the' potentialsource 142 and is connected to the cathode element 118.

The flood gun 116 is centrally located within the envelope 112 andconsists of ,at least a cathode element 164, a control grid 166 and ananode element 172. The ood gun 116 produces a high current, divergingbeam source to uniformly ood with electrons the entire surface of thestorage multiplier element 132. The cathode element 164 of the flood gun116 is provided with an exterior connection to a switching means 168.The switching means 168 is alternatively connected through a potentialsource 170 to ground (i.e. position 1) through a potential source 171 toground (i.e. position 2), or directly to ground (i.e. position 3).

Enclosing the opposite end of the envelope 112 is a face plate 174 madeof a visible light transparent Imaterial such as glass. Deposited on theinner surface of the face plate 174 is a coating 178 of a suitableilluminescent material. The coating 178 is made of a suitable phosphormaterial for emitting light in the visible region such as zine sulfideactivated with copper. The coating 178 and an electron permeable coating180 of an electrically conductive material together make up a displayele-ment 176 for visually reproducing the output signal of the device110. The coating 180 may be made of a suitable conductive material suchas aluminum and be deposited on the exposed surface of the coating 178.An external connection is made from the coating 180 of the electricalconductive material to a potential source 188 which is connected toground.

Positioned adjacent and parallel to the display element 176 is thestorage multiplier element 132 which consists of two conductive,perforated layers 152 and 154 between which has been inserted aplurality of tubes or tube means 146. On the surface of the conductivelayer 152 remote from the display element 176 there is deposited thelayer 156 of a suitable storage dielectric material having a very highresistivity such as silica or magnesium fluoride. Further, theconductive layer 152 is connected externally of the envelope 112 toground and the conductive layer 154 is connected externally of theenvelope 112 to ground through a potential source 157.

Positioned adjacent and parallel to the storage multiplier element 132is a mesh electrode 182 which is typically in the form of a line meshhaving a comparable number of openings as the storage ymultiplierelement 132. The mesh electrodeI 182 is connected externally of theenvelope 112 to ground through a potential source 184. Further, anelectrode 158 which may be formed as a layer of conductive material onthe interior surface of the envelope 112 serves to collimate theelectrons emitted from the electron gun 116 so that the electronsapproach the storage multiplier element 132 normal to the plane thereof.The collimating electrode 158 is connected externally of the envelope112 to ground through a potential source 160. In addition, the anodeelement 172 is connected to ground through a potential source 186. Inone specilic mode of operation, the potential sources 186, 160 and 184may be respectively set at 100, 150 and 200 volts positive so that theelectrons emitted from the ood gun 116 may beI properly accelerated andfocused upon the storage target element 132.

The operation of the image storage display device 110 shown in FIG. 4 issimilar to the image storage device 10 of FIG. 1 in that it requires theoperation of four steps which include (l) priming, (2) writing a patternof charges, (3) reading, and (4) erasing.

(1) Printing- During the rst step of this operating cycle, the write gun114 is biased to cutoff and the cathode element 164 of the floodingelectron gun 116 is connected by the switching means 168 (i.e.position 1) to the potential source 170 which is approximately 12 voltsnegative with respect to ground. Electrons will thus be emitted from theood electron gun 116, and focused and accelerated with an energy ofabout 12 volts over substantially the entire surface of the layer 156 ofthe storage dielectric material. Since 12 electron volts is below therst cross-over point (see FIG. 5), the bombarded surface of the layer156 of the storage multiplier element 132 will charge in a negativedirection to an equilibrium potential of about 12 volts negative withrespect to ground. It is noted that the conductive layer 152 isconnected to ground and that there will be a potential diiference acrossthe layer 156 of approximately 12 volts. Next, the switching means 168is connected to ground (i.e. position 3) so that substantially noelectrons from the flooding gun 116 can be transmitted to the storagemultiplier element 132.

(2) Writing-After the priming step, the input signal to be stored uponthe storage multiplier element 132 is applied to the write gun 114 fromthe source 138. The electrons emitted from the cathode element 118 willbe formed into a pencil-like electron beam and the current densitythereof will be modulated by the input signal applied to the controlgrid 120. The modulated electron beam is focused and accelerated tostrike the surface of the layer 156 of the storage dielectric materialwith an energy of about 22 volts negative with respect to ground, whichis below the first cross-over point. Thus, the number of secondaryelectrons emitted from the layer 156 is less than the number of primaryelectrons, and therefore the surface will charge in a negativedirection. By the application of suitable voltage to the deection plates130 and 134 associated with the write gun 114, a negative charge patternis written on the surface of the layer 156 corresponding to theinformation received from the source 138. Thus, it may be understoodthat there is a pattern of charges upon the layer 156 including portionsrepresenting a white or maximum signal on which there has been stored acharge of a potential of approximately 17 volts negative with respect toground and portions representing a minimum or a black signal upon whichthere has been disposed a charge to a potential of approximately 12volts negative with respect to ground. It is, of course, noted thatintermediate signals may be stored upon the layer 156 having chargepotentials ranging between 12 and 17 volts negative with respect toground.

(3) Reading-After a negative charge pattern has been disposed upon thesurface of the layer 156, the write gun 114 is biased to cutoff and theood gun 116 is reactivated as by disposing the switching means 168 inposition 1 so as to connect the cathode element 164 to the potentialsource 170 of approximately 12 volts negative with respect to ground.Under these conditions, the high positive potentials as applied to theconductive layer 154 and the conductive layer 180 by the potentialsources 157 and 188 respectively tend to draw electrons emitted from theooding electron gun 116 through the storage multiplier element 132 andto cause the electrons to bombard the coating 178 thereby resulting inan emission of light from the display element 176. The electric field asestablished by the pattern of charges disposed upon the layer 156 actsto control or to modulate the flow of electrons through the tubes 146;thus in those portions of the layer 156 that have been charged morenegatively, there will be less electrons owing through the tubes 146 andwhere those portions of the layer 156 are charged more positively, moreelectrons will be allowed to pass through the tubes 146 to bombard thedisplay element 176.

As the modulated electron beams enter the tubes 146, a potential ofapproximately 2,000 volts positive with respect to ground is applied asby potential source 157 to the conductive layer 154. As the electronsproceed through the tubes 146 they strike a secondary emissive materialwhich forms the inner surface of the tubes 146. Thus, the electron beamsare repeatedly multiplied due to the repeated bombardment of theinterior surface of the tubes 146. The intensified, modulated electronbeams are then accelerated as by a potential of approximately 3,000 to10,000 volts positive with respect to ground which is applied as by thepotential source 188 to the conductive layer 180. Thus, the luminescentpattern appearing on the display element 176 is a replica of the chargepattern written and stored on the layer 156 of the storage multiplierelement 132 by the write gun 114. It is particularly noted that a lesspositive voltage need be applied to the display element 176 to produce acorresponding intensity of the visual image generated thereby due to themultiplication of electrons by the storage multiplier element 132.

(4) Erasing-In order to remove the pattern of charges established uponthe layer 156 of the storage dielectric material, the write electron gun114 remains in a cutoff condition and the cathode element 164 of theflood gun 116 is connected as by switching means 168 (i.e. position 2)to the potential source 171 of approximately 300 volts negative withrespect to ground. The electrons emitted from the ood gun 116 areaccelerated with an energy of about 300 electron volts which is betweenthe first and second cross-overs of the storage material of layer 156(see FIG. 5). In this area of the curve, the number of secondaryelectrons emitted from the storage layer 156 is greater than the numberof primary electrons incident upon the surface and therefore the surfacewill charge in a positive direction. The secondary electrons emittedfrom the surface of the layer 156 are removed by the mesh electrode 182and t-he display element 176. The potential of the layer 156 willthereby be driven positively toward an equilibrium potential determinedprincipally by the potential applied to the mesh electrode 182. It isnoted that the entire surface of layer 156 is driven positively tothereby erase the pattern of charges written thereon by the electron gun114. As explained above, it will be necessary to prime the storagemultiplier element 132 in order that another pattern of charges may bewritten thereon.

In an alternative method of operating the image storage display device110, the writing of the pattern of charges upon the storage multiplierelement 132 could be achieved by writing at a potential between the rstand second cross over points. In this method, the step of priming thelayer 156 storage dielectric material will be performed as set out aboveby driving the surface of a layer 156 to a potential of 10 voltsnegative with respect to ground. This could be accomplished byconnecting the cathode element 164 of the flood gun 116 to a potentialof approximately 10 volts negative with respect to ground. Then, thewrite gun 114 is activated by applying a potential of approximately2,000 volts negative with respect to ground to the cathode element 118.The electrons emitted from the write gun 114 would be scanned as by thepair of plates 130, 134 across the surface of the layer 156. Theincident writing electron beam would in turn produce more secondaryelectrons per incident primary electron to thereby drive the surface ofthe layer 156 positively. As a result, a positive pattern of chargeswould be established upon the surface of the layer 156 ranging in apotential from minus 10 volts negative with respect to ground for thoseportions where no input signal was applied to the write gun 114 to 5volts negative with respect to ground for those portions of the surfaceof the layer 156 upon which a maximum input signal was applied. In orderto provide a visual display upon the element 176, the write gun 114 isbiased to cutoff and a potential of between zero and l volts negativewith respect to ground is applied to the vcathode element 164 of thefiood gun 116. As explained before, the electrons emitted from the fioodgun 116 are directed over the entire surface of the storage multiplierelement 132. The fiood electrons are first modulated by the pattern ofcharges disposed upon the layer 156 and are then multiplied as they passthrough the tubes 146 to thereafter be directed upon the display element176 to produce a visual output.

In the development of electron multiplying means such as the storagemultiplier element 32, there has developed a significant problem inproviding a method of fabricating the tubular or channel elements with auniform configuration and a uniform spacing between the tubularelements. Further, there has been a difficulty in providing a tubularelement having an interior surface exposed to the `bombardment ofprimary electrons with uniform secondary ernissive properties. Thus, inaccordance with the teachings of this invention, it is an importantaspect of this invention to provide an improved method of manufacturinga multiplier element and, in particularly, of forming the individualtubes or tubular means.

Referring now to FIG. 6, there is shown schematically an illustrativeprocess for fabricating the individual tubular elements and ofassembling them into a unitary multiplier element. In FIG. 6, a supplyreel 200 on which a tubular form of filament 202 to be treated is wound,freely turns as a drive roller 256 pulls the filament 202 through aseries of intermediate steps. Illustratively, the filament 202 may bemade of a suitable material having a smooth surface such as nylon andhave a diameter of approximately .001 inch corresponding to that of thetubes 46. The filament 202 is guided through an evacuated chamber 204 byidler wheels 214 and 216. Within the chamber 204 evacuated as by a pump212, a suitable, dense metallic material such as aluminum or magnesium,which is disposed within a container 208, is evaporated by a heaterelement 210 onto the filament 202. Further, the vacuum within thechamber 204 is maintained as by resilient, annular members 206 disposedat either end of the chamber for maintaining a seal between the chamberand the filament 202. The metallic substance such as aluminum isevaporated onto the filament 202 to a depth that may be easily oxidizedthroughout; specifically, the aluminum may be deposited and oxidized toa depth not in excess of 1.5 microns.

Following the application of a layer of a metallic substance, thefilament 202 is directed through a tank 240 for the purpose ofthoroughly anodizng the layer of the metallic substance. The filament202 is guided across an idler wheel 218 and about a rotating electrode242 which is immersed within a suitable electrolytic solution such asacetic or boric acid within the tank 240. The filament 202 is directedfrom the electrolytic solution by an idler wheel 220. A suitablepotential is applied between the electrode 242 and an additionalelectrode 244 also disposed within the electrolytic solution;specifically, a positive potential is applied to the electrode 242 toinsure the anodization of the metal layer. The thickness of the layer tobe anodized is dependent upon the voltage applied between the electrodes242 and 244; typically, the electrolytic constant for these particularelectrolytes is about 13 volts per angstrom of layer thickness to beanodized. In particular a voltage of approximately 750 volts would berequired to thoroughly anodize a layer of aluminum of approximately lmicron in thickness. It is pointed out, as will be emphasized later,that the formation of an aluminum oxide, a secondary ernissive materialwith a coefficient of 2 to 4, provides the necessary structural rigidityand conformity as well as a good, uniform secondary ernissive surface.

Following the anodization of the metallic layer deposited on thefilament 202, the filament 202 is drawn through an adhesive material ascontained in a tank 246.

In particular, the filament is drawn successively over the idler rollers222, 224, 226 and 228. In one illustrative process, the adhesivematerial may be ceramic material such as aluminum oxide (high alumina)disposed in a slurry solution within the tank 246. Next, the filament202 is directed as by the idler rollers 230, 232, 234, 235 and 236through a heating chamber 248 where the excess moisture within theslurry solution deposited upon the filament 202 is driven off by theheat generated by the heater elements 250. Illustratively, the heaterelements 250 are raised to a temperature slightly less than C. in orderto drive out the water contained in the adhesive slurry deposited uponthe filament 202.

Next, the filament 202 is directed as by an idler roller 238 onto thetakeup reel 256; a suitable drive unit 258 is coupled to the takeup reel256 as by a drive roller 260. After a sufiicient length of the filament202 has been wound upon the takeup reel 256, the wound filament 202 issubjected to heat provided by heater element 252 and directed thereon bya reflector 254. lllustratively, the filament 202, which is coated witha layer of a secondary ernissive material and a layer of an adhesivematerial, is heated to a temperature of up to approximately 200 C. tothereby harden the adhesive material. The wound strands of filament 202are removed from the roller 256 and sections therefrom are cut to form amultiplier element. Then, the inner, nylon filament 202 is removed as bydissolving the nylon with a solvent such as trichlorethylene,chlorinated hydrocarbons, or one of the concentrated mineral acids. Sucha solvent acts to dissolve the nylon filament without attacking theceramic material coated thereabout. Finally, the cut, assembled elementsare heated to a temperature of approximately 1000 C. to fire theadhesive material into a fused, ceramic hard structure. The final tiringor hardening treatment is performed after the filament of nylon has beenremoved because a filament of such a material cannot withstand thesehigh temperatures.

In an alternate method of fabricating the tubular elements, the layer ofsecodnary ernissive material may be formed from a solid strand of ametallic substance such as aluminum or magnesium. Typically, aluminumcould be processed so as to form a thin layer of aluminum oxide thereonto a depth of approximately 1 micron. Typically, this anodizationprocess could be performed in a manner as described above wherein thealuminum filament could be disposed within an anodization tank. Next,the aluminum filament could be coated with a layer of an adhesivematerial and wound upon a reel. The wound filament could then be bakedas at a high temperature approximately 1000" C. and cut into individualsections to form a multiplier element. Finally, the inner core ofaluminum could be dissolved as by hydrochloric acid to thereby leave aplurality of tubular elements of the aluminum oxide. The advantage ofthe use of a metallic filament is that the final firing step may beperformed before the filament is removed, thus avoiding a second heatingtreatment and possible variation of the discussions of the tubularelements.

An important aspect of this invention is the provision of a tubularelement of a secondary ernissive material that has a rigid, definedconfiguration which will withstand the winding and the cuttingoperations without deformation. Further, the interior surface of thesetubular elements does present a dense, smooth surface with secondaryemissive characteristics that are essentially uniform for each of thetubular elements. The formation of a secondary ernissive material as bythe oxidization or anodization of a metallic substance does form therequired dense, structurally rigid element with the desired uniformsecondary ernissive surface. The uniformity of secondary ernissivecharacteristics obtained by the above described method has a particularsignificance with regard to the image storage tubes of this invention.With regard to the storage tube 10 shown in FIG. 1, it is necessary toobtain an output signal which is proportional to the electron imageemitted by the photocathode element 18; thus, the provision of tubes 46having uniform secondary emissive characteristics ensures that theoutput current is uniformly multiplied and is an accurate measure of theelectron irnage emitted by the photocathode element 18. Further, it isnecessary to incorporate tubes 146 within the storage-dis play tube 110of FIG. 4 with uniform characteristics to ensure that the visual imagedisplayed upon the screen 176 has a uniform intensity ofY brightness.

While there have been shown and described what are considered to be thepreferred embodiments of the invention, modications thereto will readilyoccur to those skilled in the art. It is not desirable therefore, thatthe invention be limited to the specific arrangement shown and describedand it is intended to cover in the appended claims all suchmodifications which fall within the true spirit and scope of theinvention.

I claim as my invention:

1. A storage multiplier element comprising a plurality of tubes, each ofsaid tubes defining an axial, multiplying path which is disposed in asubstantially parallel relationship with the axial paths of the othertubes, the VYlongitudinal dimension of said tubes exceeding by a factorin excess Of l the lateral dimension of said tubes, said tubes having aninner surface exhibiting the property of emitting secondary electrons inresponse to an electron bombardment, each of said tubes having anentrance and an exit upon which there has been disposed an electricallyconductive layer, a layer of a storage material being disposed upon saidconductive layer associated with said entrance for storing a pattern ofcharges in response to an electron bombardment and for modulatingelectrons entering said entrances, and a potential source for providingan electrical field along said multiplying paths to accelerate themodulated electrons and to increase the number of the modulatedelectrons by repeated bombardments of said interior surfaces.

2. A storage multiplier element comprising a cellular structure with aplurality of tubes, saidtubes defining a multiplying path the axis ofwhich is disposed substantially parallel with the axes of the othertubes, the longitudinal dimension of said tubes exceeding by a factor inexcess of the lateral dimension of said tubes, said tubes having aninner surface exhibiting the property of emitting secondary electrons inresponse to electron bombardment and having an entrance portion into andexit portion from said path defined by said tubes, a layer ofelectrically conductive material disposed about said entrance and exitportions to allow electrons to pass into and from said tubes, and alayer of storage material disposed on said layer of electricallyconductive material associated with said entrance portions for storing apattern of charges in response to electron bombardment and formodulating said electrons entering said tubes in accordance with saidpattern of charges.

3. A storage multiplier element comprising a plurality of tubes eachdefining a multiplying path the axis of which is disposed in a parallelrelation with the axes of other tubes, the longitudinal dimension ofsaid tubes exceeding by a factor in excess of 10 the lateral dimensionof said tubes, said tubes having an inner surface exposed to said pathand made of a material selected from the group consisting of aluminumoxide and magnesium oxide for emitting secondary electrons in responseto electron bombardment, said tubes having an entrance portion into andexit portion from said path dened by said tubes and being joinedtogether so that said entrance and exit portions form intersticesbetween said tubes, a layer of electrically conductive material disposedon said interstices associated with entrance and exit portions so as toallow electrons to pass through said tubes, and a layer of storagematerial disposed on said layer of electrically conductive materialassociated with said entrance portion for storing a pattern of chargesin response to an electron bombardment and for modulating said electronsin accordance with said pattern of charges as they enter said tubes.

References Cited UNITED STATES PATENTS 4/1964 Goodrich et al. 313-10312/1966 Link et al 315-12 U.S. Cl. X.R. B15-l0, l2

